Although I’m still looking for other articles, here is one I found which I think does a nice job. From Gold Mook GT Series, "BNR34 最速の証明"(BNR34, Proof of Speed), February 2, 1999, which was published when the R34 GT-R was first introduced. It traces the history of testing at Nurburgring for the three second generation GT-Rs, and talks in general terms about the mechanical differences. And most importantly, its job is to excite and inform the reader about the BNR34!

So for the R33, the mandate was clear –to go even faster, with higher abilities. So the R33 came with ET-S PRO (active diff), 17 inch wheels, Brembos, electronic HICAS, etc. – all in all a technically much more advanced car than the R32. Thus equipped, we know that the R33 was able to shave 21 seconds off the time of the R32 – for a record setting (back in 1995) time of 7 minutes, 59 seconds, set by Dirk Schoysman. This result was heavily publicized by Nissan, the first production car to break the 8 minute barrier.
So what happened for the R34? The article does not give a recorded best time, nor does it even mention if the R34 was faster than the R33. But the interviewees reveal that, faster is not what they necessarily wanted. They also talk about the mechanical changes that were made compared to the R33, and why.

First discussed was an improvement of body rigidity. This was necessary to begin with, as in initial planning it was decided that the car would have 18 inch wheels, and there would be an increase in torque (note: at the time the article was written, the manufacturers still had to pretend that the maximum horsepower the cars produced was 280 ps – but there was no gentleman’s agreement to limit increases in torque, even though the reality is that every increase in torque also meant an increase in horsepower).
Next up were the aerodynamics. Using data from their racing experience, they first outfitted a front under-panel, which made immediate improvements. Then, of course the rear diffuser, which test driver Kato claimed “made an bigger difference than expected.” The effects were felt starting at 80kms per hour. The benefits were an increase in steering feedback, and strangely, quieter running. At Nur, the body stayed planted to the ground, and not with excessive downforce.
Strangely, these are the only two differences mentioned in this article. The rest of the article talks about testing methods (how they used a Multi-Road Simulator to test body rigidity, for example, as well as, for the first time, an onboard Marelli data logger). There is mention of course of the shortening of the wheelbase, but not on its effect, performance-wise. No mention of weight differences, nor changes to the suspension geometry, etc.
So what can we conclude so far, based on this article? Yes, there were objective improvements made to the R34 over the R33. But nothing that would make the car “faster” per say. Easier to drive, maybe. And when you think about it, I would argue that is what Nissan has done with the R35 as well – made it incredibly easy to drive fast.
As someone who enjoys actually driving his car, versus being taken for a ride, these second generation GT-Rs are the way to go. AND, on a SUBJECTIVE basis, the R33 is the best fit for me.
As before, would love to hear everyone's thoughts on this topic.
Here is a historical list of lap times by various cars at Nurburging.
http://en.wikipedia.org/wiki/List_of_N%C3%BCrburgring_Nordschleife_lap_times
Note1: Please check out my revised Spec List page (page tabs, upper-left of this page)
Note2: Apologies also to those readers who were expecting another parts review or tweak on my car. With the horrible weather and a busy schedule, have not had time to do much to my car other than keep it clean. Any spare time at night I am either working, writing for GTROC.org (follow my weekly R35 GT-R build) or trying to catch up on sleep. This however should change in the near future, with the warmer weekends ahead. I have several projects in the pipeline yet!